As shown in FIG. 1, a nuclear power station conventionally includes a reactor pressure vessel 10 with various configurations of fuel and reactor internals for producing nuclear power. For example, vessel 10 may include a core shroud 30 surrounding a nuclear fuel core 35 that houses fuel structures, such as fuel assemblies, 40. A top guide 45 and a fuel support 70 may support each fuel assembly 40. An annular downcorner region 25 may be formed between core shroud 30 and vessel 10, through which fluid coolant and moderator flows into the core lower plenum 55. For example, in US Light Water Reactor types, the fluid may be purified water, while in natural uranium type reactors, the fluid may be purified heavy water. In gas-cooled reactors, the fluid coolant may be a gas such as helium, with moderation provided by other structures. The fluid may flow upward from core lower plenum 55 through core 35. After being heated in core 35, the energetic fluid may enter core upper plenum 60 under shroud head 65.
One or more control rod drives 81 may be positioned below vessel 10 and connect to control rod blades 80 (FIG. 2) that extend among fuel assemblies 40 within core 35. Vessel 10 may be sealed and opened through upper head 95 at flange 90. With access to the reactor internals, some of fuel bundle assemblies 40 are replaced and/or moved within core 35, and maintenance / installation on other internal structures and external structures, including shroud 30 and reactor pressure vessel 10 itself may be performed inside and outside reactor 10.
FIG. 2 is an illustration of a portion of fuel core 35 from FIG. 1 showing several fuel assemblies 40 positioned about a control blade 80. During operation, control rod drive 81 maneuvers control rod blade 80 to a desired axial position among fuel assemblies 40 to obtain a desired power density. Control rod blade 80 typically has a cross or cruciform traverse cross-section; however, rods and other shapes are known control elements useable in nuclear reactors. Control rod blade 80 includes a material that absorbs neutrons of a desired spectrum, such as boron, cadmium, etc., so as to reduce neutron fluence among assemblies 40 and thus control the nuclear chain reaction. In FIG. 2, fuel bundle assemblies 40 surround the control rod blade 80, which is positioned in a central intersection surrounded by the four fuel bundle assemblies 40 in order to maximize exposure to, and thus control, fuel assemblies 40 together.
FIG. 3 is an illustration of a related art fuel assembly 40, such as assemblies 40 shown in FIGS. 2 and 3. As shown in FIG. 3, fuel assembly 40 includes multiple fuel rods 14 filled with fissile material for power generation. Fuel rods 14 are arranged in a uniform grid laterally and extend in the axial direction continuously throughout assembly 40. Fuel rods 14 are seated into a lower tie plate 16 and extend upward into an upper tie plate 17 at ends of fuel assembly 40. Fuel rods 14 are bounded by a channel 12 that forms an exterior of the assembly 40, maintaining fluid flow within assembly 40 throughout the axial length of assembly 40. Conventional fuel assembly 40 also includes one or more fuel spacers 18 at various axial positions to align and space fuel rods 14. One or more water rods 19 may also be present to provide a desired level of moderator or coolant through-flow to assembly 40.